Michael Reagan, adopted during President Reagan’s first marriage, comes out with his own book on Tuesday. It’s a polemic called “The New Reagan Revolution: How Ronald Reagan’s Principles Can Restore America’s Greatness.” Newt Gingrich, a likely 2012 Republican candidate for president, wrote the foreword.

The Ronald Reagan Presidential Foundation, closely tied to former first lady Nancy Reagan, issued its own statement, more delicate but still forceful, pushing back on the claim that he suffered from Alzheimer’s while leading the free world.

“We believe Ron has written a wonderfully warm and engaging book about life with his father, Ronald Reagan,” the foundation said. “It offers a tribute that only a son could present. As for the topic of Alzheimer’s, this subject has been well documented over the years by both President Reagan’s personal physicians, physicians who treated him after the diagnosis, as well as those who worked closely with him daily. All are consistent in their view that signs of Alzheimer’s did not appear until well after President Reagan left the White House.”

Indeed, Reagan was not officially diagnosed with Alzheimer’s until 1994. His presidency ended in January 1989.

Ron Reagan recalled the earliest signs of Alzheimer’s during an interview that aired Friday night on ABC’s “20/20,” but he also argued that it should not undercut the legacy of his father’s presidency.

In the book, he guesses that his father probably would have resigned had he known he was ill. Excerpts from the book, which doesn’t come out until Tuesday, were first published on the U.S. News & World Report’s Washington Whispers blog.

“Pray for my brother,” Michael Reagan wrote in another post on Twitter.